Wireless access devices are becoming more prevalent. Wireless access can be implemented in many different forms, including connecting a wireless access device (client) through a wireless mesh network that provides connection to a wired network. FIG. 1 shows a wireless mesh network that includes a client device 140. The wired gateway in the FIG. 1 can accept clients directly, so it can also be an access node. The client device 140 is wirelessly connected to an access node 130. The wireless access node 130 is wirelessly connected to a wired gateway 110 through another wireless access node 120. The wired gateway 110 can provide access to the internet 100 as an access node.
The transfer of information from the client 140 to the gateway 110 is generally bidirectional. That is, information flows from the client device 140 to the gateway 110 (generally referred to as upstream traffic) and information flows from the gateway 110 to the client device 140 (generally referred to as downstream traffic). The amount of data per unit time that flows between the gateway 110 and the client device 140 is called throughput. The maximum amount of data that can flow per unit time is called maximum throughput. It is desirable to maximize the throughput of wireless mesh networks.
The wireless connections 150, 160, 170 between the gateway 150, the access nodes 120, 130 and the client device 140, can be implemented with either full duplex or half duplex transceivers. Full duplex transceivers are able to transmit and receive at the same time, whereas half duplex receives can either transmit or receive at a given time. Half-duplex transceivers are typically cheaper and more easily available because they are less complex than full duplex transceivers.
Mesh networks such as the mesh network shown in FIG. 1 can suffer from interference problems. For example, the access node 130 can suffer from self-interference or interference due to transmission signals generated by other access nodes. A first dashed line 180 shows self-interference in which signals transmitted from access node 130 through channel 170 are coupled back to the access node 130 through the channel 160. Other interference is shown by dashed line 190 in which the signals transmitted from the access node 130 through the channel 170 are coupled to the access node 120 through the channel 150. This interference can reduce the maximum throughput delivered by the mesh.
Mesh networks can be constructed with omni-directional antennas to allow the relative orientations of the access nodes and clients to change with respect to each other. Omni-directional antennas, unlike directional antennas, allow access nodes and clients to communicate without having to maintain strict control over the relative locations of the access nodes and clients. However, interference between communication channels is more difficult to control with mesh networks that include omni-directional antennas.
Interference between access nodes and clients can be reduced by allocating different non-overlapping frequency spectrum to different channels that are close in proximity. For example, a first channel 150 can be allocated a first frequency spectrum channel, and a second channel 160 can be allocated a second frequency spectrum channel. Therefore, the interference between the first channel 150 and the second channel 160 can be greatly reduced. A third channel 170 can include a third frequency spectrum channel.
Actual implementations of mesh networks still suffer some interference even when different frequency spectra are allocated for different transmission channels of the mesh network. Some signal power from one channel will always couple into a neighboring channel because the signals transmitted are never completely contained within the designated channel. That is, for example, signals transmitted over the first channel 150 will always include some signal power within the second channel 160 and the third channel 170. This undesired adjacent channel signal power causes interference. Furthermore, even if the transmitted signals are completely contained within their designated channels, their relatively high power can cause loss of sensitivity for nearby receivers.
Filtering can be included within radios of the access node to filter transmitted and received signals of the radios. The filtering reduces the effects of undesired neighboring transmission channel signals. However, the filtering can add undesired cost to the access nodes.
It is desirable to have a wireless mesh network in which the throughput of the mesh network is optimized while minimizing interference and minimizing hardware costs associated with access nodes of the wireless mesh network.